Water balance is maintained through the regulation of water reabsorption by the renal collecting duct (CD) via the vasopressin (AVP) regulated water channel aquaporin-2 (AQP2). Dysfunction in AQP2 leads to diseases such as nephrogenic diabetes insipidus (polyuria) or antidiuresis syndrome (water retention), and severe fluid retention is a common ailment in cardiovascular disease. Histone deacetylase enzymes (HDACs) remove acetyl groups from lysines of histones leading to epigenetic modification of gene transcription or non-histone proteins in a post-translational manner. There is growing interest in the therapeutic use of HDAC inhibitors in cardiovascular disease because of their anti- inflammatory properties. Interestingly, a reported side effect of HDAC inhibitor use is hyponatremia, suggesting these drugs affect fluid balance. Thus, it is imperative that we gain a better understanding of the role of HDACs in body fluid balance in order to avoid potentially dangerous side effects. Our compelling preliminary data support a novel role for HDAC1 regulation of diuresis by regulating transcription and deacetylation of proteins in the CD. Our central hypothesis is that during excess water consumption, HDAC1 mediates diuresis via regulation of AQP2 apical expression by directly deacetylating AQP2, indirectly by decreasing expression of the AVP subtype 2 receptor (V2R), and indirectly by increasing in nitric oxide synthase-1 (NOS1) derived nitric oxide (NO). The following hypotheses will be tested: 1) To test the hypothesis that water balance is maintained by changes in collecting duct AQP2 acetylation and apical surface expression; 2) To test the hypothesis that hydration promotes deacetylation of AQP2 and/or downregulation of the V2R receptor via HDAC1 in the CD, thus promoting diuresis; 3) To test the hypothesis that HDAC1-dependent increases in CD NO derived from NOS1 leads to decreases in AQP2 surface expression. With the help of mentor and advisory team, I will continue on the path towards my long term goal of developing a strong, independent, research program in the field of cardio/renal physiology with a focus on addressing novel mechanisms underlying cardio/renal diseases.